U.S. patent number 4,765,827 [Application Number 07/005,130] was granted by the patent office on 1988-08-23 for metal value recovery.
This patent grant is currently assigned to Ensci, Inc.. Invention is credited to Thomas J. Clough, Arthur C. Riese, John W. Sibert.
United States Patent |
4,765,827 |
Clough , et al. |
* August 23, 1988 |
**Please see images for:
( Certificate of Correction ) ** |
Metal value recovery
Abstract
A process for at least one of (1) recovering at least one first
metal other than manganese from a first ore containing reducible
manganese, and (2) recovering at least one second metal from a
second ore containing the second metal and at least one metal
sulfide of a metal other than the second metal and manganese; the
process comprising at least one of: (A) contacting the first ore
with an aqueous composition and a material containing at least one
metal sulfide in the presence of a metal redox couple more positive
than about +0.1 versus the standard hydrogen electrode, W. M.
Latimer convention, at conditions effective to (1) chemically
reduce at least a portion of the manganese, (2) oxidize at least a
portion of the metal and/or the sulfide from the metal sulfide, and
(3) at least partially liberate the first metal from the first ore,
and recovering the first metal from the first ore; and (B)
contacting the second ore with an aqueous composition and at least
one reducible manganese-containing material in the presence of a
metal redox couple more positive than about +0.1 versus the
standard hydrogen electrode, W. M. Latimer convention, at
conditions effective to (1) chemically reduce at least a portion of
the manganese, (2) oxidize at least a portion of the metal and/or
the sulfide from the metal sulfide, and (3) at least partially
liberate the second metal from the second ore, and recovering the
second metal from the second ore.
Inventors: |
Clough; Thomas J. (Santa
Monica, CA), Sibert; John W. (Malibu, CA), Riese; Arthur
C. (Toluca Lake, CA) |
Assignee: |
Ensci, Inc. (Woodland Hills,
CA)
|
[*] Notice: |
The portion of the term of this patent
subsequent to June 21, 2005 has been disclaimed. |
Family
ID: |
21714336 |
Appl.
No.: |
07/005,130 |
Filed: |
January 20, 1987 |
Current U.S.
Class: |
75/732; 75/733;
423/DIG.4; 423/DIG.17; 423/22; 423/27; 423/29; 423/30; 423/31;
423/41; 423/49; 423/52 |
Current CPC
Class: |
C22B
3/18 (20130101); C22B 11/04 (20130101); C22B
47/00 (20130101); Y10S 423/17 (20130101); Y02P
10/234 (20151101); Y10S 423/04 (20130101); Y02P
10/20 (20151101) |
Current International
Class: |
C22B
3/18 (20060101); C22B 47/00 (20060101); C22B
3/00 (20060101); C22B 011/04 () |
Field of
Search: |
;423/27,29,30,31,41,49,52,DIG.4,DIG.17 ;75/2,11R,115,118R,121 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Tuovinen, O. H. and Kelly, D. P., "Use of Micro-Organisms for the
Recovery of Metals", International Metallurgical Reviews, vol. 19,
1974, pp. 21-31..
|
Primary Examiner: Stoll; Robert L.
Attorney, Agent or Firm: Uxa; Frank J.
Claims
The embodiments of the present invention in which an exclusive
property or privilege is claimed are as follows:
1. A process for recovering silver from an ore containing reducible
manganese comprising contacting said ore with an aqueous
composition and a material containing at least one metal sulfide in
the presence of a metal redox couple more positive than about +0.1
versus the standard hydrogen electrode, W. M. Latimer convention,
at conditions effective to (1) chemically reduce said manganese,
(2) oxidize at least one of said metal from said metal sulfide and
said sulfide from said metal sulfide, and (3) liberate said silver
from said ore, said redox couple being selected from the group
consisting of (A) at least one iron complexing agent in an amount
effective to promote the oxidation of at least one of said metal
and said sulfide from said metal sulfide, (B) at least one vanadium
component in which vanadium is present in an amount in the 5+
oxidation state effective to promote the oxidation of at least one
of said metal and said sulfide from said metal sulfide, and
mixtures thereof; and recovering said silver from said ore.
2. The process of claim 1 wherein said metal redox couple is more
positive than about +0.5 versus said standard hydrogen
electrode.
3. The process of claim 1 wherein said iron complexing agent is
derived from a material selected from the group consisting of
poly-functional amines, salts of poly-functional amines, phosphonic
acids, phosphonic acid salts, pyridine, substituted chelating
pyridine derivatives, glyoxime and salicylaldehyde derivatives,
condensed phosphates and mixtures thereof.
4. The process of claim 1 wherein said metal sulfides have a
formula of (Me)y S x wherein x and y are greater than zero and Me
is a metal selected from the group consisting of Fe, Mo, As, Cu,
Co, Ni, Sn, Sb, Bi, Pb, Zn and mixtures thereof.
5. The process of claim 1 wherein said metal sulfide is iron
pyrites.
6. The process of claim 1 wherein said contacting occurs in the
presence of added ferric ion.
7. The process of claim 1 wherein the pH of said aqueous
composition is in the range of about 0.5 to about 5.0.
8. The process of claim 1 wherein said contacting occurs in the
presence of Thiobacillus bacteria.
9. The process of claim 1 wherein said reducible manganese
component includes manganese +3, manganese +4 and mixtures
thereof.
10. The process of claim 1 wherein said contacting occurs in the
presence of at least one added oxidant.
11. The process of claim 10 wherein said added oxidant comprises
oxygen.
12. The process of claim 1 wherein said reducible manganese
component is regenerated by oxidation of a reduced manganese
component.
13. The process of claim 11 wherein said additional added oxidant
acts to oxidize a reduced manganese component to form said
reducible manganese component.
14. The process of claim 12 wherein said regeneration occurs
separately from said contacting and said regenerated reducible
manganese component is recycled to said contacting step.
15. The process of claim 3 wherein said vanadium component is a
vanadium oxide and said copper component is selected from the group
consisting of copper +2 complexes with ligands and mixtures
thereof.
16. The process of claim 1 wherein said ore and said metal
sulfide-containing material are agglomerated, and the resulting
agglomerates are placed to form a first heap which is contacted
with said aqueous composition.
17. The process of claim 16 wherein said agglomerates after said
contacting are reagglomerated and placed on a second heap which is
contacted with aqueous cyanide solution to solubilize silver.
18. The process of claim 1 wherein said metal redox couple is at
least one vanadium component in which vanadium is present in an
amount in the 5+ oxidation state effective is promote the oxidation
of at least one of said metal from said metal sulfide and said
sulfide from said metal sulfide.
19. The process of claim 10 wherein said additional added oxidant
is air.
20. The process of claim 19 wherein said metal redox couple is at
least one vanadium component in which vanadium is present in an
amount in the +5 oxidation state effective is promote the oxidation
of at least one of said metal from said metal sulfide and said
sulfide from said metal sulfide.
21. A process for recovering at least one first metal selected from
the group consisting of gold, silver, the platinum group metals and
mixtures thereof from a ore containing said first metal and at
least one metal sulfide of a metal other that manganese, said
process comprising contacting said ore with an aqueous composition
and at least one reducible manganese-containing material in the
presence of a metal redox couple more positive than about +0.1
versus the standard hydrogen electrode, W. M. Latimer convention,
at conditions effective to (1) chemically reduce said manganese,
(2) oxidize at least one of said metal and said sulfide from said
metal sulfide, and (3) liberate said first metal from said ore,
said redox couple being selected from the group consisting of (A)
at least one iron complexing agent in an amount effective to
promote the oxidation of at least one of said metal and said
sulfide from said metal sulfide, (B) at least one vanadium
component in which vanadium is present in an amount in the 5+
oxidation state effective to promote the oxidation of at least one
of said metal and said sulfide from said metal sulfide, and
mixtures thereof; and recovering said first metal from said
ore.
22. The process of claim 21 wherein said metal redox couple is more
positive than about +0.5 versus said standard hydrogen
electrode.
23. The process of claim 21 wherein said iron complexing agent is
derived from a material selected from the group consisting of
poly-functional amines, salts of poly-functioal amines, phosphonic
acids, phosphonic acid salts, pyridine, substituted chelating
pyridine derivatives, glyoxime and salicylaldehyde derivatives,
condensed phosphates and mixtures thereof.
24. The process of claim 21 wherein said metal sulfides have a
formula of (Me)y S x wherein x and y are greater than zero and Me
is a metal selected from the group consisting of Fe, Mo, As, Cu,
Ni, Sn, Sb, Bi, Pb, Zn, and mixtures thereof.
25. The process of claim 21 wherein said metal sulfide is iron
pyrites.
26. The process of claim 21 wherein said contacting occurs in the
presence of added ferric ion.
27. The process of claim 21 wherein the pH of said aqueous
composition is in the range of about 0.5 to about 5.0.
28. The process of claim 21 wherein said contacting occurs in the
presence of Thiobacillus bacteria,
29. The process of claim 21 wherein said reducible manganese
component includes manganese +3; manganese +4 and mixtures
thereof.
30. The process of claim 21 wherein said contacting occurs in the
presence of at least one added oxidant.
31. The process of claim 30 wherein said added oxidant comprises
oxygen.
32. The process of claim 21 wherein said reducible manganese
component is regenerated by oxidation of a reduced manganese
component.
33. The process of claim 31 wherein said added oxidant acts to
oxidize a reduced manganese component to form said reducible
manganese component.
34. The process of claim 32 wherein said regeneration occurs
separately from said contacting and said regenerated reducible
manganese component is recycled to said contacting step.
35. The process of claim 23 wherein said vanadium component is a
vanaduim oxide and said copper component is selected from the group
consisting of copper +2 complexes with ligands and mixtures
thereof.
36. The process of claim 21 wherein said ore and said reducible
manganese-containing material are agglomerated, and the resulting
agglomerates are placed to form a first heap which is contacted
with said aqueous composition.
37. The process of claim 36 wherein said agglomerates after said
contacting are reagglomerated and placed on a second heap which is
contacted with aqueous cyanide solution to solubilize said first
metal.
38. The process of claim 21 wherein said first metal is gold.
39. The process of claim 21 wherein said metal redox couple is at
least one vanadium component in which vanadium is present in an
amount in the +5 oxidation state effective is promote the oxidation
of at least one of said metal and said sulfide from said metal
sulfide.
40. The process of claim 30 wherein said metal redox couple is at
least one vanadium component in which vanadium is present in an
amount in the +5 oxidation state effective is promote the oxidation
of at least one of said metal and said sulfide from said metal
sulfide.
41. The process of claim 40 wherein said metal redox couple is at
least one vanadium component in which vanadium is present in an
amount in the +5 oxidation state effective is promote the oxidation
of at least one of said metal and said sulfide from said metal
sulfide.
Description
This invention relates to a process for recovering at least one
first metal, e.g., silver, from an ore containing reducible
manganese and the first metal. The invention also relates to a
process for recovering at least one second metal, e.g., gold, from
an ore containing metal sulfides and the second metal. In
particular, the invention relates to a process for recovering the
first metal and/or the second metal which involves processing the
first metal, reducible manganese-containing ore and/or the second
metal, metal-sulfide-containing ore so as to facilitate the
recovery of the first metal and/or second metal from the ore.
Reducible manganese-containing ores quite often contain metal
values which are difficult to recover because of the "locking"
nature of the manganese in the ore. For example, the occurrence of
manganese-locked silver ores has long been a problem for ore
processors. Conventional smelting can treat small, limited
quantities of manganese-locked silver ores when processing
conventional ores. The manganese must be properly slagged to
prevent attack of the crucibles. This consumes silica, increases
energy required, and contributes to metal loss in the slag.
Manganese-locked silver ores may be leached with sodium cyanide to
recover silver, but such recovery is often limited by the manganese
content. Manganese in such ores "locks" the silver in the ore by,
for example, blocking access by the sodium cyanide solution to the
silver-bearing or silver minerals.
Metal sulfide-containing ores often contain metal values, such as
gold, the platinum group metals and the like, which are difficult
to recover because of the "locking" nature of the metal sulfide in
the ore. For example, the occurrence of insoluble metal
sulfide-locked gold ores has long been a problem for ore
processors. In addition, electrum-containing ores are also
difficult to process for the recovery of precious metal values.
Use of sodium cyanide to remove silver from such manganese-locked
silver ores or to remove gold from such gold metal
sulfide-containing ores is usually uneconomical. Moreover,
stringent air pollution control regulations and low metal prices
have forced smelters to shut down or select ores from which metal
values can be recovered relatively easily. Ores which include
"locking" manganese (e.g., containing about 0.5% to about 35% by
weight of manganese) are often considered marginal and may not be
processed.
In an article entitled "The Cyanide Process for Gold and Silver
Ores" by Frank A. Seeton appearing in Deco Trefoil,
January-February, 1966, certain constituents are noted as
"cyanicides" which may be present in gold and silver-containing
ores. A "cyanicide" may be defined as a natural-occurring material
that reacts with cyanide causing abnormal cyanide consumption and
frequently influences dissolution and precipitation of gold and
silver. Copper minerals are "cyanicides" and constitute a serious
problem in cyanidation. Contents as low as 0.1 percent copper in
the ore will create excessive cyanide consumption due to the
formation of copper cyanide complexes and, in turn, have adverse
effects on gold and silver dissolution and precipitation.
Chalcopyrite is the least objectionable of the copper minerals.
Arsenic and antimony sulfides dissolve in the alkaline solution and
form compounds which will react with the oxygen in the cyanide
solution and inhibit the dissolution of gold and silver values. To
a lesser degree, zinc and nickel-bearing minerals may be
troublesome. Generally, reduced sulfur-compounds which are not
effective in leaching gold or silver.
Pyrrhotite is a common constituent of gold and silver ores and is
not only a cyanicide but also consumes oxygen in the solution due
to the decomposition of pyrrhotite. Various remedies for these
conditions have been suggested such as pre-aeration in alkaline
water solutions in the absence of cyanide and discarding the
pre-aeration solution prior to cyanidation or the use of metallic
salt in conjunction with low lime alkalinity during
cyanidation.
Commonly assigned U.S. patent application Ser. No. 858,056 and
858,369, filed Apr. 30, 1986, disclose processes for the recovery
of various metal values, e.g., silver, gold, and the platinum group
metals, involving the use of reducible manganese components. These
applications also include a more detailed discussion of certain
prior art references. Also, commonly assigned U.S. patent
application, Ser. No. 931246, filed Nov. 17, 1986, discloses a
process to reduce the sulfur content of coal and petroleum. In
certain embodiments, this process utilizes iron complexing agents,
vanadium 5+components and copper 2+components to provide sulfur
oxidation. All of these applications are incorporated in their
entireties by reference herein. There continues to be a need for
improved processing to recover metal values, in particular from
reducible manganese-containing ores and metal sulfide ores.
Therefore, one object of the present invention is to provide a
process for recovering at least one metal other than manganese from
a reducible manganese-containing ore.
An additional object of the present invention is to provide a
process for recovering at least one metal from a metal
sulfide-containing ore. Other objects and advantages of the present
invention will become apparent hereinafter.
An improved process for recovering at least one first metal other
than manganese from a first ore containing reducible manganese,
e.g., manganese generally in the plus three (+3) or four (+4)
oxidation state, and/or for recovering at least one second metal
from a second ore containing the second metal and at least one of
certain sulfides of a metal other than manganese and the second
metal has been discovered. In one broad aspect, the process
involves: containing the first ore with an aqueous composition and
a material, e.g., a metallurgical material, ore and the like,
containing at least one metal sulfide in the presence of a metal
redox couple more positive than about +0.1 versus the standard
hydrogen electrode (W. M. Latimer convention) at conditions
effective to (1) chemically reduce at least a portion of the
manganese, (2) oxidize at least a portion of the metal and/or
sulfide from the metal sulfide, and (3) at least partially liberate
the first metal from the first ore; and recovering the first metal
from the first ore. In another broad aspect, the process involves:
contacting the second ore with an aqueous composition and at least
one reducible manganese-containing material, e.g., a metallurgical
material, ore and the like, in the presence of a metal redox couple
more positive than about +0.1 versus the standard hydrogen
electrode (W. M. Latimer convention) at conditions effective to (1)
chemically reduce at least a portion of the manganese, (2) oxidize
at least a portion of the metal and/or sulfide from the metal
sulfide, and (3) at least partially liberate the second metal from
the second ore; and recovering the second metal from the second
ore. Preferably, the above-noted contacting is conducted in the
presence of a metal redox couple more positive than about +0.5
versus the standard hydrogen electrode (W. M. Latimer convention).
In one embodiment, the contacting occurs in the presence of an
additional added oxidant, more preferably a gaseous source of
oxygen, e.g., air, enriched/diluted air, oxygen and the like. In
one embodiment, the redox couple is preferably selected from at
least one of the following redox couples: (A) at least one added
iron complexing agent in an amount effective to promote the
oxidation of the metal and/or sulfide from the metal sulfide; (B)
at least one added vanadium component in which vanadium is present
in an amount in the 5+oxidation state effective to promote the
oxidation of metal and/or sulfide from the metal sulfide; (C) at
least one added copper component in which copper is present in an
amount in the 2+oxidation state effective to promote oxidation of
metal and/or sulfide from the metal sulfide; and mixtures thereof.
Both first and second ores preferably contain precious metals, such
as silver (e.g., first metal) and/or gold (e.g., second metal)
which can be recovered using the process of this invention. The
various embodiments of this invention can be practiced singly or in
any combination of embodiments, with selection and optimization
generally being a function of the ore type and desired metal value
recovered.
The benefits resulting from the process of this invention, e.g.,
improved rate of oxidation including solubilization of the metal
and/or sulfur species from the metal sulfide, and/or yield/recovery
of desired metal as a function of time, are substantial. Without
wishing to limit the invention to any specific theory of operation,
it is believed that many of such benefits result from the promoting
effect of one or more of the above metal redox couples in the
process of this invention. The promoting effect of a redox couple
allows the process to be effective, e.g., from the standpoint of
improved recovery of desired metal as a function of time, on a wide
variety of difficult to process ores.
In one embodiment, the metal sulfide has a formula of (Me)ySx
wherein x and y are greater than zero, preferably x is greater than
y and Me is a metal selected from the group consisting of Fe, Mo,
As, Cu, Co, Ni, Sn, Sb, Bi, Pb, Zn and mixtures thereof. Such metal
sulfides preferably include at least one S--S (sulfur to sulfur)
bond. Such sulfides include pyrites, metal sulfides, iron pyrites
and pyrite-like metal sulfides. Typical examples of metal sulfides
and mixed metal sulfide ores are pyrite, pyrrhotite, marcasite,
marionite, arsenopyrite, calcosite, chalcopyrite, covellite,
bornite, sphalerite, pentlandite, millerite, stibnite, orpiment and
realgar plus mixed metal sulfides. In another embodiment, the
contacting occurs in the presence of Thiobacillus ferrooxidans in
an amount effective to facilitate, e.g., generally to increase the
rate of, the liberating of the first and second metals from the
first and second ores respectively. The various embodiments are
meant to be inclusive and not exclusive. That is, the (Me)ySx of
the first embodiment may be used in conjunction with the
Thiobacillus ferrooxidans of the second embodiment. Thiobacillus
ferrooxidans are the preferred bacteria for use in the process of
this invention, although Thiobacillus thiooxidans can be employed,
e.g., either alone or in combination with other components, in an
amount effective to enhance the oxidation of sulfur species of the
metal sulfide.
The present process provides substantial advantages. For example,
the use of at least one of certain promoting metal redox couples,
preferably one or more iron complexing agents, vanadium components
and copper components (with or without complexing agents), provides
for improved contacting, e.g., to increase the rate of metal and/or
sulfide oxidation and, ultimately to improve the yield of first
metal and/or second metal recovered. The improved rate of metal
and/or sulfide oxidation also results in significant process and
cost economies. In addition, effective first and/or second,
preferably first and second, metal recoveries can be achieved
utilizing low grade (heretofore difficult to process) reducible
manganese-containing ores and relatively inexpensive, plentiful
metal sulfide-containing ores. Further the present process does not
require the addition of sulfur dioxide or hydrogen sulfide to
maintain or culture any bacteria.
The process of this invention is useful on any suitable first
metal, reducible manganese-containing ore, e.g., an ore containing
oxidized manganese. At least a portion of the manganese-bearing
minerals from the spinel group. Particularly, the process is useful
on silver, manganese-containing first ores in which at least a
portion of the silver is locked by the manganese-bearing minerals
such that at least a portion of the silver is not readily recovered
using conventional techniques, e.g., cyanide extraction. Such
silver, manganese-containing ores are "preconditioned" in the
present contacting step so that at least a portion, preferably a
major portion, of the silver is liberated from the ore. By
"liberated from the ore" is meant that the desired metal (first
and/or second metal) in the ore after the present contacting can be
more effectively recovered using conventional (preferably cyanide
extraction) processing relative to the uncontacted ore. In certain
embodiments of the process of this invention, a metal
sulfide-containing material is contacted with the
manganese-containing ore.
The second metal, metal sulfide-containing ore which is used in the
process of this invention may be suitable metallic sulfide ore.
Preferably, the second ore includes one or more iron sulfides, in
particular iron pyrites. Metal sulfide-containing second ores
useful in this invention may include other minerals or compounds in
amounts which do not substantially interfere or deleteriously
affect the present process. The metal sulfide-containing second ore
also includes one or more valuable second metals, such as gold, the
platinum group metals and mixtures thereof. The present contacting
step provides for at least partially liberating the second metal or
metals from the sulfide-containing second ore. At least a portion,
preferably a major portion of the second metal is liberated from
the second ore. This second ore containing the desired second metal
or metals, after contacting according to the present invention, is
subjected to additional processing during which the second metal or
metals are recovered from the contacted second ore.
In embodiments of the present invention in which the presence of
Thiobacillus ferrooxidans is optional, the metal sulfide is
preferably pyrites selected from a group consisting of iron
pyrites, chalcopyrite, arsenopyrite, pyrrhotite and mixtures
thereof. More preferably, the metal sulfide comprises iron
pyrites.
In embodiments of the invention which require the presence of
Thiobacillus ferrooxidans any suitable metal sulfide capable of
performing at the conditions of the present contacting step, and
preferably capable of being oxidized by the bacteria, may be used.
Because of cost, availability and performance considerations, the
preferred metal sulfide for use in these embodiments is iron
sulfide, in particular iron pyrites.
The amount of metal sulfide employed in the present contacting step
should be sufficient to provide the chemical
reduction/oxidation/first metal liberation to the desired degree.
Preferably, the amount of metal sulfide employed should be about
40% to about 250%, more preferably about 80% to 120%, of that
required to achieve the desired degree of manganese chemical
reduction. Substantial excesses of metal sulfides should be avoided
since such excesses may result in materials separation and handling
problems, and may even result in reduced recovery of the desired
first metal or metals. The amount of reducible manganese employed
in the present contacting step should be sufficient to provide the
chemical reduction/oxidation/second metal liberation to the desired
degree. Preferably, the amount of reducible manganese employed
should be about 40% to about 250%, more preferably about 80% to
120%, of that required to achieve the desired degree of metal
and/or sulfide oxidation. Substantial excesses of reducible
manganese should be avoided since such excesses may result in
materials separation and handling problems, and may result in
reduced recovery of the desired second metal or metals.
The metal sulfide component which is used in the first metal
recovery embodiment of this invention may be any metallic sulfide
ore, including arsenic, zinc, iron, cobalt, nickel, tin, lead, and
copper. The metal sulfide may be in any size or form. The metal
sulfide component may be intermixed with the manganese-containing
ore or brought in contact with the manganese-containing ore by the
aqueous, acidic composition which is in turn intermixed with the
manganese-containing ore. Metal sulfide components useful in this
invention may include other minerals or compounds in amounts which
do not substantially interfere or deleteriously affect the present
process.
In one embodiment, the present invention involves conducting the
contacting step of the present invention in the presence of at
least one iron complexing agent (iron complex) in an amount
effective to promote the oxidation of themetal and/or the sulfide
from the metal sulfide. The specific amount of iron complexing
agent employed may vary over a wide range, and depends, for
example, on the metal sulfide and complexing agent employed, and on
the degree of oxidation desired. Preferably, the mole ratio of
complexing agent to metal ion that it used to form the promoter is
in the range of about 0.01 to 5, more preferably about 0.5 to about
2.0. Preferred concentrations of iron complexing agent are in the
range of abou 150 to 10,000 ppm, more preferably about 200 to about
1,000 ppm., by weight based upon the acidic, aqueous composition,
calculated as elemental iron. It is generally convenient to provide
the iron complexing agent in combination with, preferably in
solution in, the aqueous, acidic composition used in the contacting
step.
Suitable iron complexing agents for use in this invention are
compounds which can complex ferrous and/or ferric ions, preferably
ferrous ions, to enhance the oxidizing potential of the iron redox
couple.
Convenient compilations providing stability constants of many
complexing agents for iron are provided in Martell and Calvin,
"Chemistry of the Metal Chelate Compounds," U.S. copyright 1952,
and "Stability Constants of Metal-Ion Complexes," supplement No. 1,
Special Publication No. 25, published by The Chemical Society, U.S.
copyright 1971, which material is incorporated herein in its
entirety by reference.
Examples of suitable iron complexing agents include the following:
poly-functional amines, for example, ethylenediamine, propylene
diamine, ethanol amine, glycine, and asparagine and salts thereof;
phosphonic acids and phosphonic acid salts, for example,
ethane-1-hydroxy-1, 1-diphosphonic acid; pyridine and substituted,
chelating pyridine derivatives, for example, phenanthroline and 2,
2'-bipyridyl; glyoxime and salicylaldehyde derivatives; and
condensed phosphates. Especially suitable salt forms of iron
complexing agents are the potassium, sodium and ammonium salts.
Mixtures of complexing compounds can be very desirably employed.
Particularly preferred iron complexing agents for use in the
present invention are those selected from bifunctional amines,
pyridine and substituted, chelating pyridine derivatives.
As will be recognized by those skilled in the art, the stability of
the ferrout and ferric complexes formed will often be affected by
the pH of the aqueous composition employed in the present
contacting step. Some stability of the complex or complexes may
have to be sacrificed because of the relatively low pH of the
aqueous composition during the contacting. This reduced complex
stability has surprisingly been found not to have an undue adverse
effect on sulfide and/or metal oxidation. The particular pH
employed can also affect the salt form of the complexing agent
employed, and such iron complexing salts are iron complexing agents
within the scope of this invention.
The iron complexing agents can be added to the contacting step
and/or can be formed in situ prior to or in the course of the
contacting.
In certain embodiments, the present contacting step occurs in the
presence of at least one added vanadium +5 component and/or at
least one added copper +2 component in an amount effective to
promote the oxidation of metal and/or sulfide from the metal
sulfide. Any suitable vanadium +5 component and copper +2 component
may be employed provided that such component is capable of
promoting the oxidation of the metal and/or sulfide at the
contacting conditions. Particularly preferred vanadium +5
components are vanadium pentoxide, i.e., V.sub.2 O.sub.5, and
complexes of vanadium +5. Among the particularly useful copper +2
components are copper +2 complexes with ligands such as pyridine,
imidazole and their non-deleterious chelating derivatives, such as
bydroxy, carboxyl, amino, alkyl, aryl, and halide substituents.
Such copper +2 components are particularly effective when present
in combination with an amount of ferric ion. In this embodiment,
the copper +2 component acts to enhance the overall oxidation of
the metal and/or sulfur from the metal sulfide. The vanadium +5
and/or copper +2 components can be added to the contacting step
and/or can be formed in situ prior to or in the course of the
contacting. If one or more of such components are present in the
contacting, the vanadium +5 and/or copper +2 concentration is
preferably at least about 10 ppm.,, more preferably about 50 ppm.
to about 1.0% and still more preferably about 100 ppm. to about
0.1%, by weight of the aqueous composition present during the
contacting, calculated as elemental vanadium and/or copper.
When vanadium +5 and/or copper +2 components are employed, the
reducible manganese component is preferably capable of oxidizing
and maintaining an effective amount of vanadium/copper component to
the vanadium +5 and copper +2 states at the contacting
conditions.
Any suitable aqueous composition may be employed in the present
process. The pH of the composition is preferably acidic and may
vary depending, for example, on the composition of the ore or ores
being treated, the composition of the metal sulfide-containing
material or reducible manganese-containing material being employed,
and the presence or absence of other entities during the
contacting. Preferably, the pH of the aqueous composition is in the
range of about 0.1, more preferably about 0.5, to about 5. However,
to enhance rate, the preferred pH of the aqueous composition is in
the range of about 1.5 to about 4.5, more preferably about 3.0 and
lower. Still more preferably, the pH of the aqueous composition is
in the range of about 1.5 to about 3.0, with excellent results
obtained with a pH in the range of about 1.5 to about 2.5.
If an effective amount of, for example, a Thiobacillus specie(s) is
used, it is preferred to utilize a pH of about 3 or lower,
preferably a pH of about 1.5 to about 2.5. It is believed that the
use of promoter(s) in the process of this invention allows the use
of wider ranges of pH's during processing in order to produce the
desired improved recovery of metals as a function of time.
The pH of the aqueous composition may be adjusted or maintained
during the contacting step, for example, by adding acid to the
aqueous composition.
The aqueous composition comprises water, preferably a major amount
of water. The composition is preferably substantially free of ions
and other entities which have a substantial detrimental effect on
the present process. Any suitable acid or combination of acids may
be included in, or added to, this composition to provide the
desired acidity. For example, hydrogen halides preferably hydrogen
chloride, nitric acid, phosphoric acid, sulfuric acid, metal salts
which decompose (in the aqueous composition) to form such acids,
mixtures thereof and the like may be employed. Because of cost,
availability and performance considerations, sulfuric acid is
preferred. Quantity and concentration of the aqueous composition
may be selected in accordance with the requirements of any given
ore to be treated and as may be found advantageous for any given
mode applying the process in practice.
In one embodiment, the present contacting occurs in the presence of
added ferric ion in an amount effective to facilitate the
liberating of the first metal from the first ore and/or the
liberating of the second metal from the second ore. The ferric ion
may be added to the contacting step separately, e.g., as
Fe(SO.sub.4).sub.3 and /or other components which produce the
desired amount of ferric ion when combined with the present aqueous
composition in the contacting step or may be generated in situ. In
order to more effectively control the amount of ferric ion present
and to provide improved contacting, it is preferred that the added
ferric ion be combined with the aqueous composition prior to the
present contacting step or adjusted, e.g., while recycling the
aqueous composition, during ore processing. The amount of added
ferric ion used in the present process is typically minor, when
compared to the amount of ore or ores and metal sulfide-containing
material and/or reducible manganese-containing material used, and
may vary depending on many factors, for example, the composition of
the ore or ores and of the metal sulfide-containing material and/or
the reducible manganese-containing material and the degree of first
and/or second metal liberation desired. Preferably, the added
ferric ion is present in an amount of at least about 10 ppm. (by
weight) of the aqueous composition. More preferably, the added
ferric ion is present in an amount in the range of about 0.01% to
about 1.0%, or even higher, by weight of the aqueous solution.
In one embodiment, the present contacting occurs in the presence of
at least one species of Thiobacillus bacteria in an amount
effective to facilitate the liberating of the first and second
metals from the first and second ores, respectively. Since the
contacting preferably results in at least a portion of the
manganese in the first ore or reducible manganese-containing
material being dissolved in the aqueous composition and since the
bacteria is preferably present in the acidic composition, the
bacteria are preferably tolerant (remain active) in such
manganese-containing compositions. The aqueous compositions and the
bacteria contained therein are maintained under regeneration
conditions, i.e., at conditions conducive tothe propagation of
bacteria, during the contacting step.
As the contacting step progresses, the aqueous composition (the
lixiviant solution) preferably becomes increasingly concentrated in
dissolved manganese from the first ore or reducible
manganese-containing material, in the form of manganese sulfate if
sulfuric acid is employed. Above certain high concentrations of
manganese, the buildup of manganese will in turn reduce the
activity of the Thiobacillus bacteria. In practice, the contacting
step is controlled, particularly through its initial stage, to
produce effective quantities of adequately manganese tolerant
bacteria, for example and preferably, by controlling the ratio of
ore or ores to metal sulfide-containing material or to reducible
manganese-containing material to aqueous composition and/or the
bleed rate of the manganese-containing aqueous composition to
insure a safe buildup rate of manganese ions in the aqueous
composition. By increasing the proportion of solids to liquids, the
manganese buildup rate in the aqueous composition is increased and
vice versa. The manganese concentration, the total dissolved solid,
and the bacterial activity in the aqueous composition can be
monitored on a periodic basis as an aid to process control.
In instances where it is not practicable or desirable to exercise
the required degree of control of the contacting step throughout
the period of time required for developing suitably tolerant
bacteria and where, consequently, it is preferred to commence the
contacting step with an adequate supply of suitably tolerant
bacteria, cultures of such bacteria may be prepared by known
methods. Normally, the Thiobacillus bacteria can tolerate manganese
in concentrations as high as 2.5 weight percent. In concentrations
above 2.5 weight percent, the growth of the bacteria is slowed to a
point at which bacteria become inactive. However, the bacteria can
be and preferably are acclimated to higher concentrations of
manganese ion by slowly increasing the manganese ion concentration
level in the aqueous, acidic composition. By normal acclimation
techniques, the manganese tolerance of the bacteria can be
increased to greater than about 4 weight percent. The bacteria are
preferably acclimated as much as possible and cost effective.
Alternately, Thiobacillus bacteria may be acclimated to higher
manganese levels using chemostate techniques operating in a
continuous mode.
Sources of the Thiobacillus bacteria useful in this invention
include sources such as the Americal Type Culture Center and
bacteria found to be naturally occurring in ore bodies. Of the
Thiobacillus ferrooxidans bacteria available from the Americal Type
Culture Center, cultures ATCC-14119, ATCC-19859, ATCC-21834, and
ATCC-33020 have been used in the process of this invention. All of
these cultures have been found to be satisfactory.
The pH necessary for the bacterial action may preferably be as low
as about 1.5 and as high as about 4.5 for the Thiobacillus
ferrooxidans bacteria. However, if the bacteria are acclimated to a
power pH, the pH of the aqueous composition in the present
contacting step may be adjusted accordingly.
The aqueous composition should be maintained at a temperature to
provide for effective contacting, preferably in the range of about
20.degree. C. to about 140.degree. C., more preferably about
25.degree. C. to about 110.degree. C., and still more preferably
about 25.degree. C. to about 80.degree. C., at atmospheric or at
elevated pressures, for example, up to about 500 psig, preferably
atmospheric up to about 100 psig. When the bacteria are employed,
such temperature should be such as to not unduly inhibit the growth
of or destroy the bacteria. In some instances, bacterial activity
has been maintained at a temperature as high as 75.degree. C.,
though normal strains of the bacteria are best maintained at below
about 60.degree. C. which is the preferred upper limit. While
limited activity is still apparent at 5.degree. C., the preferred
lower limit is about 15.degree. C. More preferably, for the
bacteria participation, the contacting occurs at a temperature in
the range of about 15.degree. C. to about 40.degree. C. Still more
preferably, the contacting temperature is in the range of about
20.degree. C. to about 30.degree. C. Both the temperature extremes
and the preferred temperature ranges may be adjusted if the
bacteria are acclimated to different ranges.
The bacteria are typically cultivated with nitrogen, phosphorous
and sulfate, or utilize naturally occurring nutrients. Any suitable
combination of compounds or components containing these
constituents may be used to culture the bacteria. Suitable
compounds include ammonia, ammonium sulfate, ammonium phosphate,
alkali acid phosphate mixtures thereof and the like. Preferably,
magnesium is also included in the culturing compounds or components
and suitable magnesium content may be provided by adding magnesium
sulfate.
In utilizing the process of this invention, certain precautions
should preferably be taken to improve performance. For example, the
raw materials and equipment utilized throughout the processing
circuit should normally be such as will not release or act as
bactericides under the conditions prevailing during the process.
Minerals which may be harmful to the bacteria include the elements
cobalt, zinc, nickel, copper, mercury, and molybdenum.
Concentrations of these minerals found in pyrites normally do not
exceed levels which would be harmful to the bacteria. Element
concentrations which would be harmful to the bacteria are
illustrated in Zeitzchriferology Microbiology, 12/72, 310. However,
as with the maganese, these concentrations may be exceeded by the
use of bacteria which have been acclimated to the harmful
mineral.
The action of the bacteria on metal sulfides may produce an
effective addition of sulfuric acid to the aqueous composition
during the contacting step. Without limiting this invention to any
theory or chemical/physical mechanism, it is postulated that this
reaction is as follows:
In instances where the contacting step results in reducing the
sulfuric acid content to the aqueous composition without a
corresponding decrease in the ferric ion content, hydrolysis of the
ferric sulfate is postulated to form sulfuric acid by the following
reaction:
This results in the precipitation of ferric salts. A controlled
amount of oxygen, such as oxygen from air, is present in order to
promote bacterial growth. In addition to promoting bacteria growth,
the presence of an additional oxidant such as gaseous oxygen, in
particular air, is preferred in the process of this invention and
enhances the effectiveness of the contacting step in the presence
of the metal redox couple promoters. Oxygen can be added during
contacting and is generally present in a concentration to enhance
the promoting effect and/or overall effectiveness of the
process.
Air and air containing a reduced concentration of oxygen are very
useful additional oxidants. Care should be exercised to avoid large
excesses of the additional oxidant so as to minimize reactions that
could solubilize deleterious elements, i.e., arsenic, etc. The
amount of additional oxidant employed is preferably in the range of
about 1% to about 125%, preferably about 2% to about 40% of that
needed to oxidize by one oxidation state the total amount of metal
and/or sulfur present in the ore fed to the present contacting
step.
In order to utilize normal recovery techniques for the first metal
(silver) content of a first ore, the manganese content of the first
ore does not need to be reduced or eliminated. The first metal
(silver) is at least partially liberated from the first ore. In
other words, the manganese is at least partially disassociated from
the silver, and not necessarily removed from the first ore. In
order to disassociate the manganese from the first metal (silver),
the manganese is preferably solubilized, for instance, as manganese
sulfate. Desirably, the manganese sulfate may be removed from
physical mixture with the first metal (silver) and redeposited
within the first ore such that the liquid effluent from the process
is not overly laden with the manganese sulfate since tihs sulfate
may be an environmental concern.
The present contacting results in at least a portion of the
reducible manganese component being chemcially reduced to form a
reduced manganese component. This reducible/reduced manganese
component exits the contacting zone and is separated from the ore,
in particular the contacted second ore. This manganese component
can be used on a once-through basis, or may be generated to
reducible manganese component and recycled to the contacting zone.
Such regeneration can be done by electrochemically oxidizing the
manganese component or oxidizing manganese with molecular oxygen,
preferably promoted for purposes of enhanced yield and rate, at
elevated temperatures to convert the reduced manganese component to
reducible manganese component.
The present process may be conducted on a batch or continuous
basis. The present contacting step may be conducted on a pad, with
the ore or ores to be treated situated in a heap; or in a vat, tank
or other suitable arrangement. The primary criterion for the
contacting step is that the desired manganese chemical
reduction/sulfide metal solubilization and first and/or second
metal liberation takes place. Preferably, the first metal,
manganese-containing ore and metal sulfide-containing material
and/or the second metal, metal sulfide-containing ore and reducible
manganese-containing material are brought together to form an
intimate admixture generally with the aqueous composition. If
bacteria are employed, it is preferred that this intimate admixture
also include the bacteria. If bacteria are utilized, the aqueous
composition preferably includes one or more nutrients useful by the
bacteria. One or more of these nutrients may be included with one
or more of the ores, sulfide material, reducible
manganese-containing material, intimate admixture and aqueous
composition. Additional amounts of acid and/or ferric ion may be
added during the contacting to provide the desired pH and ferric
ion concentration.
The solid ore/material remaining after the contacting step may be
subjected to any suitable metal recovery processing step or steps
for the recovery of the first metal, e.g., silver, and the second
metal, gold, the platinum group metals and the like. For example,
this solid ore/material may be neutralized with any suitable basic
material, such as white lime or milk of lime, and then subjected to
a conventional sodium cyanide extraction, followed by activated
carbon treatment and zinc dust precipitation. Alternately, the
solid ore/material after contacting can be neutralized and
subjected to an ammonium thiosulfate or an acid thiourea extraction
followed by zinc dust precipitation. Still further, the solid
ore/material after contacting can be subjected to a brine
extraction followed by ion exchange to recover the desired metal or
metals. The conditions at which these various recovery processing
steps take place are conventional and well known in the art, and
therefore are not described in detail here. However, it is
important to note that conducting the metal recovery processing on
the ore/material after the contacting of the present invention
provides improved metal recovery performance relative to conducting
the same metal recovery processing without this contacting.
One processing arrangement which provides outstanding results
involves the agglomeration of the first metal, manganese-containing
ore and the metal sulfide-containing material and/or the second
metal, metal sulfide-containing ore and the reducible
manganese-containing material. The ore and material are preferably
subjected to crushing, grinding, or the like processing to reduce
particle size to that desired optimum metallurgical liberation,
generally a maximum particle diameter of about 1/2 inch or less.
The ore and material particles are mixed with sufficient aqueous
acid (H.sub.2 SO.sub.4), and if desired, promoter and bacteria.
This intimate admixture is formed into agglomerates by conventional
processing, such as extruding, pilling, tableting and the like.
The agglomerates are placed on a pad, to form a heap which is built
up by addition of agglomerates, preferably over a period of time in
the range of about 15 days to about 60 days. During the time the
heap is being built up, and preferably for a period of time ranging
up to about 3 months, more preferably about 2 months to about 3
months after the last agglomerates are added to the heap, an
aqueous (H.sub.2 SO.sub.4) contacting composition with promoter,
and preferably adjusted for pH, ferric ion and/or the presence of
air, is made to flow through the heap, e.g., from the top to the
bottom of the heap. If bacteria are used, the aqueous composition
includes one or more nutrients for the bacteria. After contacting
the heap, the aqueous composition is collected and processed for
disposal, processed for manganese and/or sulfide metal recovery,
and/or recycled to the heap. This contacting provides another
important benefit in that at least a portion of the "cyanacides"
such as copper, which may be present in the ore and/or metal
sulfide-containing material is removed and/or deactivated. Such
"cyanacides" cause substantial increases in cyanide consumption if
present incyanide extraction processing. Therefore, removing and/or
deactivating cyanacides in the present contacting step provides for
more effective metals recovery by cyanide extraction.
After the heap/aqueous composition contacting has proceeded to the
desired extent, an aqueous basic (e.g., white lime, milk of lime or
the like basic components) composition is contacted with the heap
to neutralize the heap. After this neutralization, the agglomerates
may be placed on a second heap, which is preferably larger than the
heap previously described.
In addition, the neutralized agglomerates may be broken apart and
reagglomerated prior to being placed on the second heap to provide
for any incidental acid neutralization and/or to expose the treated
ore for subsequent cyanidation. This can be done using conventional
means, such as subjecting the agglomerates to grinding, milling or
the like processing, and then forming the second agglomerates by
extruding, tableting, pilling, pelletizing or the like
processing.
In any event, if a second, preferably larger, heap is formed on a
pad, then a dilute aqueous cyanide, preferably sodium cyanide,
solution is made to contact the second heap. Typically, this
cyanide contacting is performed in the presence of air. Preferably,
the cyanide solution is percolated through the second heap. The
cyanide solution, after being contacted with the second heap,
contains the first metal (silver) and/or the second metal. This
solution is collected and sent to conventional further processing
for recovery of the first and/or second metal.
Both heaps are preferably maintained at ambient conditions e.g., of
temperature and pressure. Also, both heaps may be built up and
worked (contacted) with the aqueous, acidic composition and the
cyanide solution for as long as the economics of the particular
application involved remain favorable.
When an agitated leach in vessels is used for the process, contact
times may vary depending, for example, on the specific ore being
contacted, the other components present during the contacting and
the degree of metal recovery desired. Contact times in the range of
about 5 minutes or less to about 48 hours or more may be used.
Preferably, the contact time is in the range of about 4 hours to
about 36 hours, more preferably about 8 hours to about 24 hours.
During this time, agitation can be advantagesouly employed to
enhance contacting. Known mechanical mixers can be employed.
While the present invention has been described with respect to
various specific examples and embodiments, it is to be understood
that the present invention is not limited thereto and that it can
be variously practiced within the scope of the following
claims.
* * * * *